1. Field of the Invention
This invention relates to a watch case and, more particularly, to a structure for fixing a back cover of a wristwatch.
2. Prior Art
In a conventional structure for fixing a back cover, the back cover is press-fitted into a case band of the wristwatch. This conventional structure depending upon simply mechanical attachment cannot maintain the fixing force of the back cover for long periods of use. Especially, a thickness of a fixing portion of the back cover cannot be sufficiently prepared in a thin wristwatch, therefore, the fixing force of the back cover is not sufficient for sealing between the back cover and the case band.
In another conventional structure for fixing a back cover, the back cover having a male screw portion at the outer periphery thereof is screwed into the case band having a female screw portion at the inner circumference thereof. It is necessary to prepare a thick back cover and case band for forming the male and female screw portions in the structure. Thus, the watch case is thick and large, and providing a thin watch case is difficult. Further, the watch case including the back cover having the male screw portion and the case band having the female screw portion must be formed in a circular form, therefore, the form of the watch case is limited to the circular form and the like.
The watch case of the wristwatch, for which an attractive appearance is essential, has grown thinner and smaller in size, in recent years. However, it is difficult to accomplish the thin watch case having a simple construction and a stable waterproof by using the structures of the above-mentioned prior art.
On this account, a structure for fixing the back cover by screws has come into widespread use. This structure is simple in construction, easy to manufacture and exhibits a stable waterproof seal. Further, such a structure is advantageous in terms of providing an attractive external appearance, and in terms of thickness and size reduction.